Figure 1.

NMDA stimulation alters mitochondrial structure and function and promotes delayed cell death. First row, Confocal fluorescence single-slice images of a typical cultured hippocampal neuron expressing mito-eYFP. The field illustrates distribution of mitochondria in the soma and in proximal processes. Under prestimulus conditions, individual eYFP-tagged mitochondria are readily seen in both the soma and processes as long bright rods. After NMDA stimulation, most eYFP-tagged mitochondria change shape to discreet, punctate dots, but many (arrows) remain rod-like. Second row, In the majority of mitochondria, normal shape returns 2 hr after stimulus removal. Shape recovery is most evident for mitochondria overlying the nucleus and in those near the origin of the process directed upward. Third and fourth rows, Confocal fluorescence images of TMRE-labeled neurons and corresponding differential interference contrast images under control conditions, immediately after NMDA stimulation, and 2 hr after stimulus removal reveal the reversible loss of mitochondrial membrane potential. Under control conditions, neurons emit a strong TMRE fluorescence signal from the cytoplasm but not from the nucleus. In neurons stimulated with NMDA, TMRE fluorescence is very low but is strong again 2 hr after stimulus removal, reflecting transient depolarization of the majority of mitochondria. Bottom row, Fluorescence images of hippocampal neurons stained with Hoechst and PI. Control cells have uniformly large nuclei with a normal chromatin pattern. At 6 hr after stimulation, degenerating cells (37 ± 5% of all neurons) can be distinguished by their small bright nuclei. At 20 hr after stimulation, degenerating cells are positive for PI (red), reflecting dead cells with disrupted plasma membranes. Scale bars, 10 μm.